High-strength copper alloy forging material

ABSTRACT

The present invention relates to a high-strength copper alloy forging material having properties of high hardness, high strength and high thermal conductivity. 
     The high-strength copper alloy forging material contains, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P, and further contains 1.5% or less of one or two or more of Cr, Mn and Zn in total, as needed, whereby appropriate amounts of Zr and P act to cause cracks to be less likely to occur in the material during working or heat treatment. After the working and the heat treatment, the forging material of the invention can have properties of high hardness, high strength and high thermal conductivity, and can be suitably used for resin injection mold materials, aircraft components and the like.

TECHNICAL FIELD

The present invention relates to a high-strength copper alloy forging material suitable for forged moldings and the like, including resin injection mold materials.

BACKGROUND ART

As alloys excellent in electrical conductivity and thermal conductivity, there have hitherto been used copper alloys such as brass (Cu—Zn-based), bronze (Cu—Sn-based), Be copper and Corson alloy (Cu—Ni—Si-based). In particular, Be copper, Corson alloy and the like have been used for resin injection mold materials, aircraft components and the like requiring strength and hardness, together with thermal conductivity. However, the above-described Be copper has concerns about toxicity of dust generated at the time of melting or working thereof, so that replacements therefor have been demanded. Further, for the Corson alloy, higher thermal conductivity, higher strength and higher hardness have been demanded.

Furthermore, generally in the Cu alloys, cracks easily occur at the time of forging or heat treatment, so that there is also demanded improvement in ductility, in addition to hot workability.

As a measure for increasing strength and improving bending workability in foil bands of the copper alloys, there has recently been proposed copper alloys in which Mg, Sn, Ti, Zr, Al, Mn and the like are added to Cu—Ni—Si-based copper alloys (see PTLs 1 to 5). Mg and Sn dissolve in solid in a matrix to improve the strength. Ti, Zr, Al and Mn form compounds with sulfur, because of their strong affinity to sulfur, thereby decreasing segregation of sulfides to grain boundaries, which is responsible for hot-working cracks.

The copper alloy foil bands as shown in PTLs 2, 3 and 5 have a bending workability and a strength exceeding those of conventional copper alloy foil bands by adding Sn, Mn, Zr and the like and repeating hot rolling and cold rolling, or hot drawing and cold drawing, before and after solution treatment and aging treatment.

CITATION LIST Patent Literature

PTL 1: JP-A-2006-9108

PTL 2: JP-A-2008-196042

PTL 3: JP-A-2008-223136

PTL 4: JP-A-2008-266787

PTL 5: JP-A-2010-106363

SUMMARY OF INVENTION Technical Problem

However, when Cu copper moldings are produced, working and forming are mainly performed by hot forging. Accordingly, in the case where rolling or drawing as performed in foil band production cannot be employed, even when forged moldings are produced using compositions as shown in PTLs 2, 3 and 5, the high strength is not obtained.

In order to obtain the high strength, it is effective to increase the amounts of Ni and Si added. However, thermal conductivity or hot workability is deteriorated with an increase in the Ni or Si amount. Further, a crystallized material formed during coagulation or a precipitate formed during heat treatment increases to decrease ductility after the heat treatment.

The invention has been made against the background of the above circumstances, and an object thereof is to provide a high-strength copper alloy forging material which is usable for forged moldings and the like, including resin injection mold materials, and can provide properties of high hardness, high strength, high ductility and high thermal conductivity.

Solution to Problem

In order to solve the above-described problems, in the invention, an appropriate amount of Zr having an effect of suppressing precipitation of Ni₂Si on crystal grain boundaries to increase ductility is allowed to be contained in a Cu—Ni—Si-based alloy. Further, an appropriate amount of P which has an effect of increasing the density of fine precipitations and also forms a compound with Ni, Si and Zr, is allowed to be contained therein, which makes it possible to obtain a material having properties of high hardness, high strength, and high thermal conductivity.

According to a first aspect of the invention, there is provided a high-strength copper alloy forging material comprising, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P.

According to a second aspect of the invention, there is provided a high-strength copper alloy forging material comprising, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P, and further comprising 1.5% or less of one or two or more of Cr, Mn and Zn in total.

According to a third aspect of the invention, in the first or second aspect, the high-strength copper alloy forging material has a 0.2% yield strength of 650 MPa or more, an elongation of 5% or more and an electrical conductivity of 30% IACS or more.

Advantageous Effects of Invention

According to the invention, cracks are less likely to occur in a material during working and heat treatment, and there can be obtained the high-strength copper alloy forging material having properties of high hardness, high strength, and high thermal conductivity.

DESCRIPTION OF EMBODIMENTS

Reasons for composition limitations of the respective components in the invention will be described below. Incidentally, all the contents of the following components are indicated by mass %. Further, “mass %” and “weight %” have the same meaning.

-   Ni: 3 to 7.2% -   Si: 0.7 to 1.8%

Ni and Si form precipitate particles of an intermetallic compound which is mainly composed of fine Ni₂Si, by performing aging treatment, and significantly increase the strength of the alloy. Further, with precipitation of Ni₂Si in the aging treatment, electrical conductivity is improved, and thermal conductivity is improved. However, when the Ni concentration is less than 3% and the Si concentration is less than 0.7%, the desired strength is not obtained. Further, when the Ni concentration exceeds 7.2% and the Si concentration exceeds 1.8%, Ni₂Si, Ni₅Si₂ and the like are crystallized or precipitated in large amounts at the time of forging, resulting in easy occurrence of cracks at the time of forging or heat treatment. In addition, when the Ni concentration exceeds 7.2%, the electrical conductivity is also decreased, and the thermal conductivity is decreased. Considering the balance of the productivity and properties, the lower limit of the Ni concentration is preferably 3.5%, and the upper limit thereof is preferably 6.6%. The lower limit of the Si concentration is preferably 0.8%, and the upper limit thereof is preferably 1.7%. Incidentally, the Ni/Si ratio is preferably from 3.8 to 4.6. In the case of departing this ratio, excessive Ni or Si is dissolved in solid in a Cu matrix to decrease the thermal conductivity.

-   Zr: 0.02 to 0.35%

Zr forms a compound with sulfur, because of its strong affinity to sulfur, and decreases segregation of a sulfide to grain boundaries, which is responsible for working cracks (hot-working cracks), thereby improving workability (hot workability). On the other hand, as a result of intensive research of the present inventors, it has been found that diffusion of Ni or Si is suppressed by containing Zr to decrease Ni₂Si precipitated on the grain boundaries, thereby improving ductility after the aging. In order to obtain this effect, Zr is allowed to be contained in an amount of 0.02% or more. However, when contained in an amount of more than 0.35%, productivity or the properties are deteriorated by increases and coagulation of crystallized materials such as Zr oxide and Ni₂SiZr. Accordingly, the upper limit thereof is 0.35%. Considering the balance of the productivity and the properties, the lower limit thereof is preferably 0.05%, and the upper limit thereof is preferably 0.3%.

-   P: 0.002 to 0.05%

P improves the strength by increasing the density of fine precipitates, and further forms a compound with Ni, Si and Zr, in which a slight amount of P is contained in Ni₂Si, Ni₂SiZr or the like, thereby increasing the hardness. In order to obtain these effects, P is allowed to be contained in an amount of 0.002% or more. However, when contained in an amount of more than 0.05%, the thermal conductivity is largely decreased. Accordingly, the upper limit thereof is 0.05%. For the same reason, the lower limit thereof is preferably 0.01%, and the upper limit thereof is preferably 0.04%.

-   Cr, Mn and Zn: 1.5% or less in total

At least one of Cr, Mn and Zn is allowed to be contained as desired.

Cr forms an intermetallic compound with Si, and has effects of improving the strength and miniaturizing crystal grains. Mn forms a compound with sulfur, because of its strong affinity to sulfur, and decreases segregation of a sulfide to grain boundaries, which is responsible for working cracks (hot-working cracks), thereby improving workability (hot workability). Zn improves the strength by solid-solution hardening. Further, when it is possible to use inexpensive brass scrap at the time of dissolution, the production cost can be reduced. However, when Cr, Mn and Zn are excessively contained in the total amount, the thermal conductivity is decreased. It is therefore preferred that the total amount of Cr, Mn and Zn is 1.5% or less.

More preferably, the total amount of Cr, Mn and Zn is 1.0% or less. Further, when at least one of Cr, Mn and Zn is allowed to be contained, the total amount thereof is preferably 0.1% or more.

The high-strength copper alloy forging material of the invention has the above-described metal composition, and the balance is composed of Cu and unavoidable impurities.

The high-strength copper alloy forging material of the invention can be produced by an ordinary method.

The copper alloy used in the invention can be ingoted by an ordinary method. For example, it is possible to melt a material under a vacuum atmosphere, an inert atmosphere, an atmospheric atmosphere or the like to obtain an ingot. The atmosphere is preferably the vacuum atmosphere or the inert atmosphere. However, the copper alloy can also be ingoted, for example, in an atmospheric high-frequency furnace. Further, secondary melting using an electroslag remelting furnace or the like may be performed. It is also possible to obtain a plate material by a continuous forging method.

The copper alloy is subjected to working as needed. The contents of the working are not particularly limited in the invention, and even when any working method is used, it is possible to obtain the properties of the invention. Incidentally, considering the productivity, the working is preferably hot working, and further preferably hot working performed at 600° C. or more. However, it is also possible to obtain the properties similar to those of the hot working even by working at room temperature. Further, the working may be a combination of the hot working and cold working. Furthermore, as the working, forging is preferred, and hot forging is more preferred. It is still more preferred that the hot forging is performed at 600° C. or more. As a forging method, there can be employed a known method such as pressing, hammering or rolling.

It is also possible that the copper alloy material worked is subjected to solution treatment after or during the working. Conditions of the solution treatment include, for example, maintaining at 800 to 1,000° C. for 1 to 10 hours, and thereafter cooling at a cooling rate of 5° C./sec or more in a temperature range of 500° C. or more, in order to sufficiently dissolve Ni and Si in solid.

The copper alloy material worked can be subjected to aging treatment after the solution treatment or after the working. Conditions of the aging treatment include, for example, maintaining at 400 to 500° C. for 1 to 30 hours.

The resulting high-strength copper alloy material has properties such as a 0.2% yield strength of 650 MPa or more, an elongation of 5% or more, and an electrical conductivity of 30% IACS or more.

Incidentally, the high-strength copper alloy forging material of the invention has excellent properties as a forging material. However, in the composition of the invention, even a casting material not subjected to the above-described working such as the forging can provide properties such as good ductility.

EXAMPLES

Examples of the invention will be described below.

Raw materials were blended so as to give component compositions (including other unavoidable impurities) of Table 1, and melted in a vacuum induction melting furnace to prepare alloys of 100 mm (diameter)×200 mm (length). These alloys were subjected to hot forging using a hammer at 900° C. to form plate materials having a thickness of 25 mm. After maintaining at 970° C. for 4 hours, solution treatment by water cooling was performed. Thereafter, aging treatment suitable for materials of the respective compositions was performed at 400 to 500° C. for 1 to 30 hours to obtain sample materials.

TABLE 1 Component (% by mass) Aging Sample Material Total of Cr, Ni/Si Conditions No. Cu Ni Si Zr P Cr Mn Zn Mn and Zn Ratio (° C. × hr) Example 1 Balance 4.16 0.95 0.09 0.018 — — — — 4.38 475° C. × 3 hr 2 Balance 5.15 1.14 0.16 0.017 4.52 475° C. × 3 hr 3 Balance 4.83 1.12 0.08 0.004 0.43 0.19 0.33 0.95 4.31 450° C. × 10 hr 4 Balance 7.20 1.80 0.22 0.034 — — — — 4.00 450° C. × 10 hr 5 Balance 3.70 0.92 0.27 0.048 0.02 — — 0.02 4.02 475° C. × 3 hr 6 Balance 4.10 0.98 0.09 0.016 0.02 0.40 — 0.42 4.18 475° C. × 3 hr 7 Balance 3.10 0.74 0.03 0.020 — — — — 4.19 475° C. × 3 hr 8 Balance 5.04 1.17 0.32 0.049 — 0.20 0.50 0.70 4.31 450° C. × 10 hr 9 Balance 6.60 1.65 0.12 0.003 0.40 — — 0.40 4.00 450° C. × 10 hr Comparative 10 Balance 7.30 1.57 — — — — — — 4.65 425° C. × 30 hr Example 11 Balance 4.24 0.99 — — — — — — 4.28 450° C. × 1 hr 12 Balance 8.37 0.93 — — — — — — 9.00 475° C. × 3 hr 13 Balance 3.77 0.95 0.16 — — — — — 3.97 475° C. × 3 hr 14 Balance 4.25 0.93 — 0.055 — — — — 4.57 500° C. × 1 hr 15 Balance 4.85 1.18 0.36 0.023 0.49 0.50 0.58 1.57 4.11 450° C. × 10 hr 16 Balance 7.77 1.87 0.10 0.022 0.42 — — 0.42 4.16 450° C. × 10 hr 17 Balance 2.20 0.55 0.01 0.002 — — — — 4.00 450° C. × 1 hr 18 Balance 8.12 2.05 0.12 0.030 — — — — 3.96 450° C. × 10 hr 19 Balance 5.33 1.39 0.08 0.006 3.03 0.22 0.15 3.40 3.83 450° C. × 10 hr

As to the sample materials prepared, evaluations shown below were performed.

(Tensile Test)

An ordinary-temperature tensile test was performed on the respective sample materials based on JIS Z2201 (2010) and JIS Z2241 (2010) to evaluate the 0.2% yield strength (Y. S.), the tensile strength (T. S.), the elongation and the reduction of area. The measurement results are shown in Table 2.

(Vickers Hardness)

For the respective sample materials, the Vickers hardness was measured at a load of 5 kg based on JIS Z2244 (2010). The measurement results are shown in Table 2.

(Thermal Conductivity)

For the respective sample materials, the electrical conductivity was measured. As shown in the Wiedemann-Franz law, the thermal conductivity has an approximately proportional relationship to the electrical conductivity, so that the thermal conductivity can be evaluated by the electrical conductivity. The measurement results are shown in Table 2.

TABLE 2 Reduction Vickers Electrical Sample Material 0.2% Y.S. T.S. Elongation of Area Hardness Conductivity No. (MPa) (MPa) (%) (%) (Hv) (% IACS) Example 1 667 772 8.8 19.0 266 36.1 2 728 809 7.2 20.8 291 35.1 3 750 806 13.2 19.5 296 35.0 4 676 781 6.6 16.0 315 30.2 5 733 789 11.0 22.0 288 31.0 6 699 766 8.1 16.2 264 36.1 7 689 755 6.5 13.0 268 40.0 8 781 866 5.9 18.1 321 33.4 9 651 766 10.0 16.3 292 33.1 Comparative 10 513 607 2.4 5.9 277 31.2 Example 11 610 620 1.8 5.9 253 37.7 12 623 764 4.6 10.5 264 29.6 13 616 717 7.6 15.4 255 35.2 14 735 813 1.8 5.2 301 33.2 15 762 830 4.1 13.6 302 29.2 16 740 855 3.6 11.0 322 28.5 17 460 520 6.9 16.2 203 52.5 18 760 856 2.5 8.3 333 23.2 19 712 811 3.0 9.2 297 29.0

As shown in Table 2, the sample materials of Examples of the invention had a 0.2% yield strength of 650 MPa or more, an elongation of 5% or more and an electrical conductivity of 30% IACS or more, and further had a hardness equivalent to or more than that of the sample materials of Comparative Examples.

As described above, according to the invention, it has been revealed that the excellent properties of increasing the strength, the ductility and the hardness while maintaining the high electrical conductivity, namely the high thermal conductivity, are obtained by containing appropriate amounts of Zr and P in the Ni—Si—Cu alloy.

The invention has been described in detail with reference to specific embodiments thereof. However, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2011-030660 filed on Feb. 16, 2011, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

According to the high-strength copper alloy forging material of the invention, appropriate amounts of Zr and P act to cause cracks to be less likely to occur in the material at the time of working or heat treatment. After the working and the heat treatment, the forging material of the invention can have the properties of high hardness, high strength and high thermal conductivity, and can be suitably used for resin injection mold materials, aircraft components and the like. 

1. A high-strength copper alloy forging material comprising, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P.
 2. A high-strength copper alloy forging material comprising, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P, and further comprising 1.5% or less of one or two or more of Cr, Mn and Zn in total.
 3. The high-strength copper alloy forging material according to claim 1, having a 0.2% yield strength of 650 MPa or more, an elongation of 5% or more and an electrical conductivity of 30% IACS or more.
 4. The high-strength copper alloy forging material according to claim 2, having a 0.2% yield strength of 650 MPa or more, an elongation of 5% or more and an electrical conductivity of 30% IACS or more.
 5. A high-strength copper alloy forging material consisting of, in mass %, 3 to 7.2% of Ni, 0.7 to 1.8% of Si, 0.02 to 0.35% of Zr and 0.002 to 0.05% of P, and further comprising 1.5% or less of one or two or more of Cr, Mn and Zn in total. 